The preparation of dialkyl oxalate esters by the homogeneous catalyzed oxidative carbonylation of alcohols in the presence of metal salt catalysts, redox agents, dehydrating agents and other compounds such as amines, carbonates, nitrates, hydroxides and ureas is well known. An article by Donald M. Fenton and Paul J. Steinwand, Journ. of Org. Chem., Vol. 39, Nos. 5, 1974, pp. 701-704 describes a general mechanism for the oxidative carbonylation of alcohols to yield dialkyl oxalates using a palladium redox system, oxygen and dehydrating agents. Typical prior art patents disclosing homogeneous catalyzed oxidative carbonylation of alcohols to prepare oxalate esters are U.S. Pat. Ser. Nos. 3,393,136; 3,994,960; 4,005,129; 4,005,130; 4,076,949; 4,118,589 and 4,281,174 as well as West German Patent No. 2,213,435 and West German Offenlegungschrift No. 2,601,139.
The present invention provides a much improved process for the production of dialkyl oxalates by employing an insoluble easily recoverable heterogeneous catalyst for the oxidative carbonylation of alcohols.
U.S. Pat. Ser. No. 4,229,591 describes a process for the preparation of a diester of oxalic acid by contacting an ester of nitrous acid or an alcohol and a nitrogen oxide or hydrate thereof in the gaseous phase in the presence of a solid catalyst containing palladium or a salt thereof such as palladium on activated carbon.
Japanese Kokai 75-157,311 discloses the preparation of oxalic acid esters by reacting a C.sub.1 to C.sub.20 monohydric alcohol, carbon monoxide and molecular oxygen in the presence of a supported Group VIII metal and a Group IB, IIB, III, IV, V, VI, and VIIIB metal, aluminum, iron, cobalt or nickel.
U.S. Pat. Ser. No. 4,039,572 discloses the preparation of diesters of dicarboxylic acids by the oxidative carbonylation of olefins and alcohols using a carrier supported catalyst consisting of (1) a platinum group metal compound and (2) a compound of a metal having an atomic number of not less than 22 which has been reduced to a metal and has a ratio of (2) to (1) of from 0.0005:1 to 10:1 gram atoms.
The oxalate products of this invention have many commercial applications and are used as solvents, dye intermediates, for the preparation of pharmaceuticals as well as feedstock for hydrogenation to ethylene glycol by, for example, the process described in U.S. Pat. Ser. No. 4,112,245.